Aluminum alloy composition for simplified semi-solid casting process and method of semi-solid casting

ABSTRACT

An aluminum alloy having about 0.03 wt % to about 0.50 wt % Niobium (Nb); about 0.03 wt % to about 0.50% Vanadium (V); about 0.03 wt % to about 0.50% Titanium (Ti), greater than 0 wt % to about 0.50 wt % Boron (B); and the balance is Aluminum (Al) and impurities. The alloy includes a weight percent ratio of (Nb+V)/Ti from about 1 to about 5, preferably from about 2 to about 3. The alloy may include a weight percent ratio (Nb+V+Ti)/B from about 1 to about 15, preferably from about 5 to about 10. The aluminum alloy may be form by incorporating 1 part master alloy, grain refiner, having about 1.5 wt % to about 4.0 wt % Niobium (Nb); from about 0.5 wt % to about 2.0% Titanium (Ti), and from about 0.2 wt % to about 0.8 wt % Boron (B) to about 27 to 80 part conventional aluminum alloy, by weight.

The present disclosure relates to aluminum alloys, more particularly to aluminum alloys for semi-solid casting.

The casting of a metal into a useful shape involves heating the metal to a temperature above its melting point, placing the molten metal into a mold, and cooling the metal to a temperature below its melting point. The metal solidifies and takes the shape of the mold, and is thereafter removed from the mold. Semi-solid casting is a known metal casting process that uses a metal pour that is in a partially solid and partially liquid slurry, also known as a semi-solid slurry. Aluminum components manufactured by semi-solid casting, particularly in high pressure die casting processes, are desirable in the aircraft, telecommunication, and automobile industries due to the relative lower porosity, lower weight, and higher strength that is characteristic of semi-solid casted components as compared to liquid aluminum casted components.

Semi-solid aluminum casted components have traditionally been produced by thioxcasting, a process which utilizes a pre-cast billet having a globular microstructure. Induction heating is typically used to heat the precast billets to the semi-solid temperature range, and die casting machines are used to inject the semi-solid slurry into hardened steel dies. A disadvantage of thioxcasting is that it is an expensive and time consuming process due to the additional steps of producing precast billets and heating the precast billets to the semi-solid temperature range.

An alternative to thioxcasting is rheocasting, which is a process of cooling liquid aluminum into the semi-solid temperature range, while vigorously agitating the liquid aluminum to generate globular microstructures, primary alpha-Al grains, for semi-solid forming. Rheocasting generates the semi-solid slurry directly from the liquid, thus eliminating the steps of producing and induction heating precast billets. However, oxidation and inclusions may form in the semi-solid slurry and entrapped in the finished casting during the cooling and agitating steps of the rheocasting process. Furthermore, rheocasting requires the semi-solid slurry to be produced and transported to the casting dies.

Thus, while current semi-solid aluminum casting processes and aluminum casting alloys used in such processes achieve their intended purpose, there is a continue need for a more efficient semi-solid casting process and aluminum alloy to enable such a process.

SUMMARY

According to several aspects, an aluminum alloy composition suitable for semi-solid casting. The aluminum alloy includes about 0.03 wt % to about 0.50 wt % Niobium (Nb); about 0.03 wt % to about 0.50% Vanadium (V); about 0.03 wt % to about 0.50% Titanium (Ti), and a remainder, or balance, comprising of Aluminum (Al) and impurities.

In an additional aspect of the present disclosure, the aluminum alloy further includes a weight percent ratio of (Nb+V)/Ti from about 1 to about 5, preferably from about 2 to about 3.

In another aspect of the present disclosure, the aluminum alloy further includes greater than 0 wt % to about 0.50 wt % Boron (B).

In another aspect of the present disclosure, the aluminum alloy further includes a weight percent ratio of (Nb+V+Ti)/B from about 1 to about 15, preferably from about 5 to 10.

In another aspect of the present disclosure, the aluminum alloy further includes from about 4.00 wt % to about 10.00 wt % Silicon (Si), from about 0.01 wt % to about 3.00 wt % Copper (Cu), from about 0.10 wt % to about 1.00 wt % Magnesium (Mg); and from about 0.01 wt % to about 0.03 wt % Strontium (Sr).

According to several aspects, a method of semi-solid casting is disclosed. The method includes heating an aluminum alloy until the aluminum alloy transform into a liquid aluminum alloy; cooling the liquid aluminum alloy until the liquid aluminum alloy transform into a semi-solid aluminum alloy; pouring the semi-solid aluminum alloy into a casting die; and cooling the semi-solid aluminum alloy until the semi-solid aluminum alloy transform into a solid aluminum alloy within the casting die. The aluminum alloy enabling the method includes about 0.03 wt % to about 0.50 wt % Niobium (Nb); about 0.03 wt % to about 0.50% Vanadium (V); about 0.03 wt % to about 0.50% Titanium (Ti), and a remainder comprising Aluminum (Al) and impurities.

In an additional aspect of the present disclosure, the aluminum alloy further includes a weight percent ratio of (Nb+V)/Ti from about 1 to about 5, preferably from about 2 to about 3.

In another aspect of the present disclosure, the aluminum alloy further comprises greater than 0 wt % to about 0.50 wt % Boron (B).

In another aspect of the present disclosure, the aluminum alloy further includes a weight percent ratio of (Nb+V+Ti)/B from about 1 to about 15, preferably from about 5 to about 10.

In another aspect of the present disclosure, the aluminum alloy further includes about 4.00 wt % to about 10.00 wt % Silicon (Si); about 0.01 wt % to about 3.00 wt % Copper (Cu); about 1.00 wt % Magnesium (Mg); about 0.03 wt % Strontium (Sr); greater than 0.0 wt % but less than or equal to about 0.50% Manganese (Mn), and greater than 0.0 wt % but less than or equal to about 0.50% Chromium (Cr).

In another aspect of the present disclosure, the step of heating the solid aluminum alloy until the aluminum alloy transform into a liquid aluminum alloy includes heating the solid aluminum alloy to a liquidus range between about 30° C. to about 80° C.

In another aspect of the present disclosure, the step of cooling the liquid aluminum alloy until the aluminum alloy transform into a semi-solid aluminum alloy includes cooling the liquid aluminum alloy at a rate greater than 5° C. per second.

According to several aspects, a master alloy is disclosed. The master alloy may be incorporated into a conventional aluminum alloy in a ratio of 1 part master alloy to 27 to 80 part conventional alloy, by weight, to produce an aluminum alloy suitable for semi-solid casting. The master ally includes about 1.5 wt % to 4.0 wt % Niobium (Nb); about 0.5 wt % to 2.0 wt % Titanium (Ti), about 0.2 wt % to about 0.8 wt % Boron (B); and a remainder comprising Aluminum (Al) and impurities.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a table showing an aluminum alloy composition suitable for semi-solid casting, according to an exemplary embodiment;

FIG. 2 is a table showing a grain refiner composition, according to an exemplary embodiment;

FIG. 3 is a magnified view of a surface finish of a laboratory sample of an aluminum alloy without grain refiner elements;

FIG. 4 is a magnified view of a surface finish of a laboratory sample of an aluminum alloy having grain refiner elements, according to an exemplary embodiment; and

FIG. 5 is a flow chart depicting the steps of a method of semi-solid aluminum casting.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. The illustrated embodiments are disclosed with reference to the drawings, wherein like numerals indicate corresponding parts throughout the several drawings. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular features. The specific structural and functional details disclosed are not intended to be interpreted as limiting, but as a representative basis for teaching one skilled in the art as to how to practice the disclosed concepts.

Referring to FIG. 1, is a table showing the composition of an aluminum alloy that enables a simplified semi-solid casting process. The aluminum alloy includes, by weight percent (wt %), from about 4.00 wt % to about 10.00 wt % Silicon (Si); from about 0.10 wt % to about 0.50 wt % Iron (Fe); from about 0.01 wt % to about 3.00 wt % Copper (Cu); from about 0.10 wt % to about 1.00 wt % Magnesium (Mg); from about 0.03 wt % to about 0.50 wt % Niobium (Nb); from about 0.03 wt % to about 0.50% Vanadium (V); from about 0.03 wt % to about 0.50% Titanium (Ti), from greater than 0 wt % to about 0.50 wt % Boron (B); from about 0.01 wt % to about 0.03 wt % Strontium (Sr); greater than 0.0 wt % but less than or equal to about 0.50 wt % Manganese (Mn), greater than 0.0 wt % but less than or equal to about 0.50 wt % Chromium (Cr); and the balance is Aluminum (Al) and impurities.

It is preferable that Mg is between about 0.3 wt % to about 0.5 wt % to enable the formation of Magnesium Silicide (Mg₂Si) precipitates. It is preferable that Cu is between about 0.3 wt % to about 1.0 wt % to enable the formation of Q-phase precipitates. It is preferable that Si is between about 5.0 wt % to about 8.0 wt % for a wide solidus-liquidus range in the semi-solid casting process. The preferred range of Fe is determined based on the ductility requirement of the produced casting.

Nb, V, Ti, and B are included in the aluminum alloy for grain refinement by forming globular microstructure. It was found that certain combinations of weight ratios of Nb, V, Ti, and B provides exceptional grain refinement in the aluminum alloy that enables the aluminum alloy to be used in semi-solid casting without the need for the additional steps of pre-casting a billet and reheating the billet to melt temperature; or the steps of cooling liquid aluminum into the semi-solid temperature range, while vigorously agitating or swirling the liquid aluminum to generate globular microstructure necessary for semi-solid.

The combined weight percentages of Nb and V to weight percentage of Ti ratio [(Nb+V)/Ti] should be controlled to be from about 1 to about 5; preferably from about 2 to about 3. In other words, the combined wt % of Nb and wt % of V is about 1 wt % to 5 wt %, preferably from 2 wt % to 3 wt %, for every 1 wt % of Ti enables the aluminum alloy suitable for simplified semi-solid casting.

The combined weight percentage of Nb, V, and Ti to weight percent of B ratio [(Nb+V+Ti)/B] should be controlled to be from about 1 to about 15; preferably from about 5 to about 10. In other words, the combined wt % of Nb, wt % of V, and wt % of Ti is about 1 wt % to 15 wt %, preferably from about 5 wt % to 10 wt %, for every 1 wt % of B also enables the aluminum alloy suitable for simplified semi-solid casting.

Referring to FIG. 2, is a table showing the composition of a grain refiner for producing the aluminum alloy to enable the simplified semi-solid casting process. The grain refiner, also referred to a master alloy, may be introduced to commercially available aluminum alloys including, but not limited to, A380, A383, and A360 aluminum alloys, to convert the commercially available aluminum alloy to form globular microstructures. The master alloy includes from about 1.5 wt % to about 4.0 wt % Niobium (Nb); from about 0.5 wt % to about 2.0% Titanium (Ti), from about 0.2 wt % to about 0.8 wt % Boron (B); and the balance is Aluminum (Al) and impurities.

The master alloy may be incorporated into a commercially available aluminum alloy at a ratio from about 1:80 to 1:27 by weight to produce the presently disclosed aluminum alloy. In other words, an aluminum alloy suitable for simplified semi-casting process may be produced by incorporating 1 part master alloy to about 27 to 80 part conventional aluminum alloy, by weight.

FIG. 3 shows a magnified view of a surface finish of a laboratory sample of an aluminum alloy 300 without grain refiner elements, according to an exemplary embodiment. The aluminum alloy 300 exhibits dendrite microstructure 302, which is not suitable for semi-solid casting.

FIG. 4 shows a magnified view of a surface finish of a laboratory sample of an aluminum alloy 400 having fine grain microstructure 402, according to an exemplary embodiment. The fine grain microstructure 402 are finer than the dendrite microstructure 302 of FIG. 3.

FIG. 5 is a flow chart depicting the steps of a method of semi-solid aluminum casting 500 using the improved aluminum alloy having the composition shown in FIG. 1. The method includes: step 502, heating a solid alloy until the solid alloy transform into a liquid alloy; step 504, cooling the liquid alloy until the liquid alloy transform into a semi-solid alloy and pouring the semi-solid alloy into a casting die; and step 506, cooling the semi-solid alloy until the semi-solid alloy transforms into a solid alloy within the casting die.

Step 502 of heating the solid alloy until the solid alloy transform into a liquid alloy includes heating the solid alloy to a liquidus range between about 30° C. to about 80° C. Step 504 of cooling the liquid alloy until the alloy transform into a semi-solid alloy includes cooling the liquid alloy at a rate greater than 5° C. per second. The cooling rate enables the formation of globular microstructures as shown in FIG. 4.

Numerical data have been presented herein in a range format. “The term “about” as used herein is known by those skilled in the art. Alternatively, the term “about” includes +1-0.05% by weight”. It is to be understood that this range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. While examples have been described in detail, those familiar with the art to which this disclosure relates will recognize various alternative designs and examples for practicing the disclosed method within the scope of the appended claims.

The description of the present disclosure is merely exemplary in nature and variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure. 

What is claimed is:
 1. An aluminum alloy comprising: about 0.03 wt % to about 0.50 wt % Niobium (Nb); about 0.03 wt % to about 0.50% Vanadium (V); about 0.03 wt % to about 0.50% Titanium (Ti), and a remainder comprising Aluminum (Al) and impurities.
 2. The aluminum alloy of claim 1, further comprising a weight percent ratio of (Nb+V)/Ti from about 1 to about
 5. 3. The aluminum alloy of claim 2, wherein the weight percent ratio of (Nb+V)/Ti is from about 2 to about
 3. 4. The aluminum alloy of claim 1 further comprising greater than 0 wt % to about 0.50 wt % Boron (B).
 5. The aluminum alloy of claim 4, further comprising a weight percent ratio (Nb+V+Ti)/B from about 1 to about
 15. 6. The aluminum alloy of claim 5, wherein the weight percent ratio (Nb+V+Ti)/B is from about 5 to about
 10. 7. The aluminum alloy of claim 4 further comprising about 4.00 wt % to about 10.00 wt % Silicon (Si).
 8. The aluminum alloy of claim 7 further comprising about 0.01 wt % to about 3.00 wt % Copper (Cu).
 9. The aluminum alloy of claim 8 further comprising about 0.10 wt % to about 1.00 wt % Magnesium (Mg).
 10. The aluminum alloy of claim 4, further comprising about 0.01 wt % to about 0.03 wt % Strontium (Sr).
 11. A method of semi-solid casting, comprising: heating an aluminum alloy until the aluminum alloy transform into a liquid aluminum alloy; cooling the liquid aluminum alloy until the liquid aluminum alloy transform into a semi-solid aluminum alloy; pouring the semi-solid aluminum alloy into a casting die; and cooling the semi-solid aluminum alloy until the semi-solid aluminum alloy transform into a solid aluminum alloy within the casting die; wherein the aluminum alloy comprises: about 0.03 wt % to about 0.50 wt % Niobium (Nb); about 0.03 wt % to about 0.50% Vanadium (V); about 0.03 wt % to about 0.50% Titanium (Ti), and a remainder comprising Aluminum (Al) and impurities.
 12. The method of claim 11, wherein the aluminum alloy further comprises a weight percent ratio of (Nb+V)/Ti from about 1 to about
 5. 13. The method of claim 12, wherein the weight percent ratio of (Nb+V)/Ti is from about 2 to about
 3. 14. The method of claim 11, wherein the aluminum alloy further comprises greater than 0 wt % to about 0.50 wt % Boron (B).
 15. The method of claim 14, wherein the aluminum alloy further comprises a weight percent ratio of (Nb+V+Ti)/B from about 1 to about
 15. 16. The method of claim 15, wherein the weight percent ratio of (Nb+V+Ti)/B is from about 5 to about
 10. 17. The method of claim 16, wherein the aluminum alloy further comprises: about 4.00 wt % to about 10.00 wt % Silicon (Si); about 0.01 wt % to about 3.00 wt % Copper (Cu); about 1.00 wt % Magnesium (Mg); about 0.03 wt % Strontium (Sr); greater than 0.0 wt % but less than or equal to about 0.50 wt % Manganese (Mn), and greater than 0.0 wt % but less than or equal to about 0.50 wt % Chromium (Cr).
 18. The method of claim 17, wherein heating the aluminum alloy until the aluminum alloy transform into a liquid aluminum alloy includes heating the solid aluminum alloy to a liquidus range between about 30° C. to about 80° C.
 19. The method of claim 18, wherein cooling the liquid aluminum alloy until the liquid aluminum alloy transform into a semi-solid aluminum alloy includes cooling the liquid aluminum alloy at a rate greater than 5° C. per second.
 20. A grain refiner for aluminum alloys, comprising: about 1.5 wt % to 4.0 wt % Niobium (Nb); about 0.5 wt % to 2.0 wt % Titanium (Ti), about 0.2 wt % to about 0.8 wt % Boron (B); and a remainder comprising Aluminum (Al) and impurities. 